Clay Mineralogy and Mica‐Vermiculite Layer Charge Density Distribution in the Switzerland Soils of Indiana

Abstract A study was made of the weathering of mica inherited from Ordovician limestone and calcareous shales in two (I and II) Switzerland soils, which belong to the Typic Normudalf, fine, mixed mesic family. X‐ray and physico‐chemical studies of the clay fraction showed that the solum of Switzerland I had an average of 24% mica and 35% vermiculite and the solum of Switzerland II was 40% mica and 24% vermiculite. Layer charge density calculated from the ratio Σ(CEC + total K)/m 2 clearly showed the decrease in charge density moving from the parent material upward in the soil profiles. The degree of swelling of the vermiculite on solvation was a function of this charge density. Magnesium‐saturated, glycerol‐solvated samples remained at 14.2A; Mg‐saturation and ethylene glycolation expanded some vermiculite to 16 to 16.5A; Ca‐saturated and glycerol treatment resulted in expansion of vermiculite to 17A; and K‐saturation and air drying readily collapsed most of the vermiculite to 10 to 10.3A.